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Abstract:

Provided is a manufacturing method for a briquetted solid fuel that can
reduce the briquetting cost while maintaining the strength of the
briquetted product. A mixed oil that includes a heavy oil and a solvent
oil, and a porous coal are mixed to obtain a slurry. The slurry is
dewatered by heating to obtain a dewatered slurry. Solvent oil is
separated from the dewatered slurry to obtain a cake, the cake is heated,
and solvent oil is further separated from the cake to obtain a modified
coal. Moisture is added to the modified coal to obtain a moist modified
coal with a moisture content of 3 wt % to 10 wt %, and then the moist
modified coal is briquetted under pressure.

Claims:

1. A method for manufacturing a briquetted solid fuel comprising: a
mixing step of mixing a mixed oil including a heavy oil and a solvent oil
with a porous coal to obtain a slurry; an evaporation step of dewatering
the slurry by heating to obtain a dewatered slurry; a solid-liquid
separation step of separating the solvent oil from the dewatered slurry
to obtain a cake; a drying step of heating the cake to further separate
the solvent oil from the cake to obtain a modified coal; a moisture
addition step of adding moisture to the modified coal to obtain a moist
modified coal with a moisture content of 3 wt % to 10 wt %; and a
briquetting step of briquetting the moist modified coal under pressure.

2. The method for manufacturing a briquetted solid fuel according to
claim 1, wherein, in the moisture addition step, a pulverized coal
obtained by pulverizing the porous coal is mixed with the modified coal.

3. The method for manufacturing a briquetted solid fuel according to
claim 1, wherein, in the moisture addition step, waste water obtained in
the evaporation step is supplied to the modified coal.

4. The method for manufacturing a briquetted solid fuel according to
claim 2, wherein, in the moisture addition step, waste water obtained in
the evaporation step is supplied to the modified coal.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a method for manufacturing a
briquetted solid fuel using a porous coal, such as brown coal, as a
starting material.

BACKGROUND ART

[0002] With respect to a method for manufacturing a solid fuel using a
porous coal, such as brown coal, as a starting material, the
manufacturing method described in Patent Document 1 has been
conventionally known. The method for manufacturing a solid fuel described
in Patent Document 1 is characterized by mixing a mixed oil including a
heavy oil component and a solvent oil component with a porous coal to
obtain a starting material slurry, heating the slurry to dewater the
porous coal and to impregnate the pores of the porous coal with the mixed
oil including the heavy oil component and the solvent oil component, and
then solid-liquid separating and drying the slurry.

[0003] In the method for manufacturing a solid fuel described in Patent
Document 1, moisture in the pores of the porous coal is evaporated by
heating the starting material slurry (i.e., mixture of the mixed oil
including a heavy oil component and a solvent oil component with the
porous coal). At the same time, the inside of the pores is covered with
the mixed oil including the heavy oil component. Finally, the pores are
filled with the mixed oil, in particular, the heavy oil component
preferentially. Consequently, adsorption of oxygen to active sites in the
pores and oxidation are suppressed, and thus spontaneous combustion of
the porous coal is suppressed. Furthermore, the heavy oil component is
filled in the pores by the heating, resulting in an increase in the
calorific value of the porous coal. Hence, according to the method for
manufacturing a solid fuel described in Patent Document 1, it is possible
to obtain a solid fuel having a low moisture content, low spontaneous
combustibility, and an increased calorific value.

[0004] However, in the method for manufacturing a solid fuel described in
Patent Document 1, since the modified coal (solid fuel) after being
subjected to the drying step is in powder form, a problem occurs with
respect to its transportation. Specifically, use of the modified coal in
powder form may result in an increase in transportation costs and may
cause dust pollution because of the low bulk density, leakage during
transportation, and fly loss. Consequently, it is desirable to briquette
the modified coal in powder form using a briquetting machine. In this
process, the modified coal in powder form cannot be briquetted unless
under high pressure. Therefore, it has been a problem to reduce the
briquetting cost. Note that, if the strength of briquettes is not high
enough, the briquettes will be easily pulverized during handling.

[0005] As the technique for briquetting a modified coal in powder form,
for example, the method for manufacturing a briquette coal described in
Patent Document 2 has been conventionally known. In the manufacturing
method described in Patent Document 2, starch is added to a coal in
powder form, mixing is performed, and the resulting mixture is briquetted
under pressure. That is, in this method, starch is used as a binder.
[0006] Patent Document 1: Japanese Unexamined Patent Application
Publication No. 7-233383 [0007] Patent Document 2: Japanese Unexamined
Patent Application Publication No. 2003-64377

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

[0008] However, in the briquetting method described in Patent Document 2
in which starch is used as a binder, it is necessary to add starch at
least in an amount of several percent to a coal in powder form, and such
addition of starch in an amount of several percent is not realistic in
terms of the briquetting cost.

[0009] The present invention has been achieved under the circumstances
described above, and it is an object of the present invention to provide
a method for manufacturing a briquetted solid fuel that can reduce the
briquetting cost while maintaining the strength of the briquetted
product.

Means for Solving the Problems

[0010] As a result of diligent research in order to solve the problems
described above, the present inventors have found that by adjusting the
moisture content of a modified coal after being subjected to a drying
step to 3 wt % to 10 wt %, and briquetting the modified coal under
pressure, it is possible to manufacture a briquetted product (briquetted
solid fuel) having high strength without using a binder, such as starch,
which can solve the problems described above. The present invention has
been completed on the basis of the finding.

[0011] That is, according to the present invention, a method for
manufacturing a briquetted solid fuel includes a mixing step of mixing a
mixed oil including a heavy oil and a solvent oil with a porous coal to
obtain a slurry, an evaporation step of dewatering the slurry by heating
to obtain a dewatered slurry, a solid-liquid separation step of
separating the solvent oil from the dewatered slurry to obtain a cake, a
drying step of heating the cake to further separate the solvent oil from
the cake to obtain a modified coal, a moisture addition step of adding
moisture to the modified coal to obtain a moist modified coal with a
moisture content of 3 wt % to 10 wt %, and a briquetting step of
briquetting the moist modified coal under pressure. Here, the moisture
content refers to the percentage (mass basis) of water contained in a
mixture of a modified coal and a pulverized porous coal, and obtained by
dividing the mass of water contained in the mixture of the modified coal
and the pulverized porous coal by the mass of the mixture. In the case
where the pulverized porous coal is not contained, the moisture content
refers to the percentage (mass basis) of water contained in the modified
coal, and obtained by dividing the mass of water contained in the
modified coal by the mass of the modified coal. Furthermore, the modified
coal refers to a coal which has been modified by reducing the percentage
of moisture so as to increase the calorific value per unit mass.

[0012] Furthermore, in the present invention, in the moisture addition
step, preferably, a pulverized coal obtained by pulverizing the porous
coal is mixed with the modified coal. Thereby, the cost of the product
can be reduced. The reason for this is that the moisture of the
pulverized coal which is not required to be subjected to modification
treatment can be used as moisture adding means in the moisture addition
step. Consequently, the moisture addition step can be carried out simply
by mixing the modified coal after being subjected to modification
treatment and the pulverized coal which has not been subjected to
modification treatment, using a known device, such as a mixer.

[0013] Furthermore, in the present invention, in the moisture addition
step, preferably, waste water obtained in the evaporation step is
supplied to the modified coal. For example, the waste water can be
supplied by spraying to the modified coal. Thereby, it is possible to
obtain an effect of decreasing the amount of water to be treated in the
waste water treatment facilities of the plant.

Advantages

[0014] According to the present invention, because of its constitutional
features, in particular, by adding moisture to the modified coal which
has been subjected to the drying step to obtain a moist modified coal
with a moisture content of 3 wt % to 10 wt %, and briquetting the moist
modified coal under pressure, bonds between particles can be
strengthened. As a result, it is possible to manufacture a briquetted
solid fuel having high strength without using a binder, such as starch.
That is, it is possible to reduce the briquetting cost while maintaining
the strength of the briquetted product.

BRIEF DESCRIPTION OF DRAWINGS

[0015]FIG. 1 is a flow chart showing a method for manufacturing a
briquetted solid fuel according to an embodiment of the present invention
and also a block diagram of a manufacturing apparatus for a briquetted
solid fuel.

[0016]FIG. 2 is a graph showing the influence of mixtures of modified
coal and pulverized porous coal on the crushing strength relative to the
roll power.

[0017]FIG. 3 is a graph showing the relationship between the moisture
content of mixtures of modified coal and pulverized porous coal and the
maximum crushing strength of briquettes which are briquetted products.

[0027] Best modes for carrying out the present invention will be described
below with reference to the drawings.

[0028]FIG. 1 is a flow chart showing a method for manufacturing a
briquetted solid fuel according to an embodiment of the present invention
and also a block diagram of a manufacturing apparatus 100 for a
briquetted solid fuel. As shown in FIG. 1, the manufacturing apparatus
100 includes a pulverizing unit 1 for pulverizing a porous coal (starting
material coal), a mixing unit 2 for mixing the porous coal pulverized in
the pulverizing unit 1 with a mixed oil including a heavy oil and a
solvent oil, a preheating unit 3 for preheating a slurry obtained in the
mixing unit 2, an evaporating unit 4 for dewatering the slurry, a
solid-liquid separating unit 5 for mechanically separating the solvent
oil from the dewatered slurry obtained in the evaporating unit 4, a final
drying unit 6 for heating a cake separated in the solid-liquid separating
unit 5 to further separate the solvent oil from the cake, a moisture
adding unit 7 for adding moisture to the modified coal in powder form
obtained in the final drying unit 6, and a briquetting unit 8 for
briquetting under pressure the moist modified coal obtained in the
moisture adding unit 7. The individual steps in the method for
manufacturing a briquetted solid fuel according to the embodiment will be
described in detail below.

(Pulverization Step)

[0029] First, a porous coal (starting material coal) is fed to the
pulverizing unit 1 and pulverized. Here, the porous coal (starting
material coal) to be fed to the pulverizing unit 1 is, for example, a
so-called low-rank coal having a moisture content of 30 wt % to 70 wt %
and desired to be dewatered. Examples of such a porous coal include brown
coal, lignite, and sub-bituminous coal. Examples of the brown coal
include Victorian coal, North Dakota coal, and Berga coal. Examples of
the sub-bituminous coal include West Banko coal, Binungan coal,
Samarangau coal, and Ecocoal coal. Furthermore, the pulverized porous
coal has a particle size of, for example, about 0.05 to 3 mm, and an
average particle size of about several hundred micrometers. Furthermore,
wt % refers to % by mass (mass ratio). In addition, in the case where a
porous coal (starting material coal) originally having a small particle
size is carried in, it is not particularly necessary to pulverize the
porous coal (starting material coal).

(Mixing Step)

[0030] Next, a mixed oil including a heavy oil and a solvent oil is mixed
with the pulverized porous coal in the mixing unit 2 to obtain a slurry.
The term "heavy oil" refers to a heavy fraction, such as a vacuum
residual oil, that substantially has no vapor pressure at, for example,
400° C. or oil containing a large amount (specifically, 50 wt % or
more) of the heavy fraction. The term "solvent oil" refers to an oil that
dissolves and disperses a heavy oil. As the solvent oil, in view of
affinity with the heavy oil, the handling property as the slurry, ease of
penetration into pores, and the like, for example, a light oil fraction
is used. Taking the stability at the moisture evaporation temperature
into consideration, it is recommended to use a petroleum-derived oil
having a boiling point of 100° C. to 300° C. Examples of
the petroleum-derived oil include kerosene, light oil, and fuel oil. By
mixing the heavy oil and the solvent oil, a heavy oil-containing mixed
oil is produced. By using such a heavy oil-containing mixed oil, the
heavy oil-containing mixed oil exhibits adequate fluidity and penetration
of oil into the pores of the porous coal is promoted.

[0031] The mixing unit 2 is constituted by a mixing tank for receiving and
mixing the mixed oil and the porous coal, an agitator provided on the
mixing tank, and the like.

(Evaporation Step)

[0032] Next, the slurry obtained in the mixing unit 2 is preheated in the
preheating unit 3, and then dewatered in the evaporating unit 4 to obtain
a dewatered slurry. The slurry is heated, for example, to 70° C.
to 100° C. in the preheating unit 3, and then fed to an
evaporation tank in the evaporating unit 4, in which the moisture
contained in the porous coal in the slurry is evaporated to dewater the
slurry. Simultaneously with the dewatering treatment, the pores of the
porous coal are impregnated with the mixed oil, and the pores are filled
with the heavy oil component preferentially. Furthermore, the moisture
contained in the porous coal in the slurry is discharged as waste water
from the evaporating unit 4.

[0033] The preheating unit 3 is constituted by a heat exchanger and the
like. The evaporating unit 4 is constituted by an evaporation tank for
receiving the slurry obtained in the mixing unit 2 and evaporating the
moisture of the slurry, an agitator provided on the evaporation tank, a
heat exchanger for heating the slurry, and the like. As the heat
exchanger, a multitubular heat exchanger, a plate-type heat exchanger, a
spiral type heat exchanger, or the like is used.

(Solid-Liquid Separation Step)

[0034] Next, the solvent oil is mechanically separated from the dewatered
slurry to obtain a cake. The dewatered slurry is fed to a solid-liquid
separator in the solid-liquid separating unit 5 and subjected to
solid-liquid separation. As the solid-liquid separator, for example, from
the standpoint of improving the separation efficiency, a centrifugal
separator is used in which the dewatered slurry is separated into the
cake and the solvent oil by a centrifugal separation method. It may also
be possible to use a solid-liquid separator that uses a sedimentation
method, a filtration method, an expression method, or the like.

(Drying Step)

[0035] The cake separated in the solid-liquid separation step is still wet
because of the mixed oil. Therefore, the cake is heated in the final
drying unit 6 to further separate the solvent oil. Thereby, the cake is
converted into a modified coal in powder form. The final drying unit 6 is
constituted by a drying machine, a gas cooler, and the like. As the
drying machine, a drying machine capable of heating an object to be
treated while continuously transporting the object to be treated inside,
and for example, a steam tube type dryer having a plurality of heating
steam tubes axially disposed on an inner surface of a drum is used.

[0036] The cake is heated in the drying machine, and the oil component, in
particular, the solvent oil component in the cake is evaporated. The
evaporated solvent oil component is transferred by a carrier gas from the
drying machine to the gas cooler. The solvent oil component transferred
to the gas cooler is condensed in the gas cooler and recovered.

(Recycling Step)

[0037] The solvent oil separated and recovered from the dewatered slurry
or the cake in the solid-liquid separating unit 5 and the final drying
unit 6 is returned as a recycling oil to the mixing unit 2. The solvent
oil returned to the mixing unit 2 is reused for adjustment of the slurry
in the mixing unit 2. Furthermore, the recycling oil to be returned to
the mixing unit 2 is mostly composed of the solvent oil component, but
the recycling oil contains a slight amount of the heavy oil component.

(Moisture Addition Step)

[0038] Moisture is added to the modified coal in powder form obtained
through the drying step to obtain a moist modified coal with a moisture
content of 3 wt %, to 10 wt % in the moisture adding unit 7. In order to
add moisture to the modified coal, there are at least two methods. In the
first method, moisture is added by mixing the starting material porous
coal pulverized in the pulverizing unit 1 with the modified coal in
powder form discharged from the final drying unit 6. In this method, the
moist modified coal is a mixture of the modified coal obtained through
the drying step and the pulverized starting material porous coal. That
is, the moist modified coal contains not only the modified coal obtained
through the drying step but also the pulverized starting material porous
coal. In the second method, moisture is added by spraying waste water
from the evaporating unit 4 to the modified coal in powder form
discharged from the final drying unit 6. One of these two methods only
may be used, or both methods may be used in combination. Alternatively,
moisture may be added to the modified coal in powder form by a method
other than the methods described above.

[0039] The moisture adding unit 7 is constituted by a moisture addition
tank for receiving and agitating the modified coal in powder form, an
agitator provided on the moisture addition tank, and the like.

(Briquetting Step)

[0040] Next, the moist modified coal with a moisture content of 3 wt % to
10 wt % is briquetted under pressure in the briquetting unit 8. The
modified coal briquetted into briquettes is used as a briquetted solid
fuel. The briquetting unit 8 is constituted by a double roll briquetting
machine and the like.

[0041] In the method for manufacturing a briquetted solid fuel according
to the embodiment, in briquetting into a solid fuel, instead of a binder,
inexpensive water, in particular, waste water discharged in the
manufacturing method is used, and therefore, the briquetting cost can be
reduced. Furthermore, by setting the moisture content to a predetermined
amount such as that described above, the strength of the briquetted
product can be maintained.

Example

[0042] Next, experimental results on briquetting of modified coal will be
described. In this experiment, modified coals with various moisture
contents were produced, and the influence of the moisture content on
briquettability was studied. In this experiment, moisture was added by
mixing a pulverized starting material porous coal to a modified coal in
powder form obtained through a drying step. First, the mixing ratio of
pulverized porous coal to modified coal obtained through the drying step,
and the moisture content in the mixture of modified coal and pulverized
porous coal are shown in Table 1.

[0043] The moisture content in the pulverized porous coal, as a starting
material, alone was 30.7%. Furthermore, in [Table 1], in the mixture in
which the mixing ratio of pulverized porous coal is 100%, the ratio of
modified coal obtained through the drying step is zero, and the ratio of
pulverized porous coal is 100%. Furthermore, in the mixture in which the
mixing ratio of pulverized porous coal is 0%, the ratio of modified coal
obtained through the drying step is 100%, and the ratio of pulverized
porous coal is zero.

[0044] Next, when the six samples shown in [Table 1] are briquetted under
pressure using a double roll briquetting machine, the relationship
between the crushing strength of briquettes and roll power per unit
number of revolutions of the double roll briquetting machine is shown in
FIG. 2. FIG. 2 is a graph showing the influence of the moisture content
of mixtures of modified coal and pulverized porous coal on the crushing
strength relative to the roll power. In FIG. 2, the solid diamond, the
solid square, and the solid triangle represent data of samples in which
the moisture content of the mixture is 0%, 3.1%, and 6.1%, respectively,
and the open triangle, the open square, and the open diamond represent
data of samples in which the moisture content of the mixture is 9.2%,
15.4%, and 30.7%, respectively.

[0045] As shown in FIG. 2, the crushing strength of briquettes relative to
the roll power per unit number of revolutions of the roll increases as
the mixing ratio increases when the mixing ratio of pulverized porous
coal to modified coal is up to 30% (the moisture content in the mixture
is up to 9.2%). However, when the mixing ratio is 50% and 100% (the
moisture content in the mixture is 15.4% and 30.7%), as the roll power
exceeds the predetermined value, the crushing strength of briquettes
tends to decrease. That is, when the mixing ratio is 50% and 100% (the
moisture content in the mixture is 15.4% and 30.7%), the crushing
strength of briquettes does not increase sufficiently compared with the
other samples.

[0046] Furthermore, regarding the effect of decreasing the roll power due
to mixing of pulverized porous coal, for example, in order to obtain
briquettes with a crushing strength of 10 kg, a roll power of about 0.18
kW/rpm (extrapolated value) is required in the case of modified coal
alone (mixing ratio of pulverized porous coal: 0%). When the mixing ratio
of pulverized porous coal to modified coal is 30% (moisture content in
mixture: 9.2%), the roll power is about 0.14 kW/rpm, resulting in a power
saving of about 20%. Note that as the roll power increases, the pressure
in briquetting under pressure increases.

[0047] As described above, in the case of modified coal alone (mixing
ratio of pulverized porous coal: 0%), the roll power for obtaining
briquettes with a crushing strength of 10 kg was found by extrapolation.
The reason for this is that, in the case of modified coal alone (mixing
ratio of pulverized porous coal: 0%), even if the roll power was
increased to about 0.16 kW/rpm or more, it was not possible to obtain
briquettes with good briquettability.

[0048] Next, the maximum crushing strength of briquettes realized in
mixtures with various moisture contents by changing the roll power per
unit number of revolutions of a double roll briquetting machine is shown
in FIG. 3. FIG. 3 is a graph showing the relationship between the
moisture content of mixtures of modified coal and pulverized porous coal
and the maximum crushing strength of briquettes which are briquetted
products.

[0049] As shown in FIG. 3, when the moisture content of the mixture of
modified coal and pulverized porous coal is 3 wt % to 10 wt %, the
maximum crushing strength of briquettes exceeds 20 kg.

[0050] As described above, by adding moisture to modified coal which has
been subjected to the drying step to obtain a moist modified coal with a
moisture content of 3 wt % to 10 wt %, and briquetting the moist modified
coal under pressure, bonds between particles can be strengthened. As a
result, it is possible to manufacture a briquetted solid fuel having high
strength without using a binder, such as starch. That is, it is possible
to reduce the briquetting cost while maintaining the strength of
briquettes.

[0051] In addition, by using pulverized starting material porous coal in
powder form in order to add moisture to modified coal, the amount of
porous coal to be treated in the mixing step to the drying step
decreases. When the amount of porous coal to be treated in the mixing
step to the drying step decreases, the amount of a mixed oil including a
heavy oil and a solvent oil to be consumed decreases, and it is possible
to decrease the capacity of equipment in the individual steps. Thus, the
manufacturing cost of the briquetted solid fuel can be reduced.

[0052] Furthermore, by using waste water from the evaporating unit 4 in
order to add moisture to modified coal, it is possible to decrease the
amount of waste water discharged from the system. As a result, the
treatment cost of waste water discharged from the system can be
suppressed, leading to a reduction in the manufacturing cost of the
briquetted solid fuel in the entire plant.

[0053] The embodiments of the present invention have been described above.
However, it is to be understood that the present invention is not limited
to the embodiments described above, and various alterations are possible
within the scope of the invention described in claims.